The present disclosure is generally directed, in various embodiments, to coatings for print heads. More particularly, the disclosure relates to a coating for a front face of an ink jet printhead, such as an anti-fouling coating for ink jet faceplates. Additionally, disclosed herein is a coating that prevents wetting, drooling, and flooding of ink, such as ultra-violet curable ink and solid ink on an ink jet printhead front face.
Fluid ink jet systems generally include one or more printheads having a plurality of ink jets from which drops of fluid are ejected towards a recording medium. The ink jets of a printhead typically receive ink from an ink supply chamber or manifold in the printhead that, in turn, receives ink from a source, such as a melted ink reservoir or an ink cartridge. Each ink jet may include a channel having one end in fluid communication with the ink supply manifold. The other end of the ink channel generally has an orifice or nozzle for ejecting drops of ink. The nozzles of the ink jets may be formed in an aperture or nozzle plate that has openings corresponding to the nozzles of the ink jets. During operation, drop ejecting signals activate actuators in the ink jets to expel drops of fluid from the ink jet nozzles onto the recording medium. By selectively activating the actuators of the ink jets to eject drops as the recording medium and/or printhead assembly are moved relative to one another, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium. An example of a full width array printhead is described in U.S. Patent Publication No. 2009/0046125, which is hereby incorporated by reference herein in its entirety. An example of an ultra-violet curable ink that can be jetted in such a printhead is described in U.S. Patent Publication No. 2007/0123606, which is hereby incorporated by reference herein in its entirety. An example of a solid ink which can be jetted in such a printhead is the Xerox ColorQube™ cyan solid ink available from Xerox Corporation.
One difficulty faced by fluid ink jet systems is wetting, drooling or flooding of inks onto the printhead front face. This may occur as a result of ink contamination of the printhead front face. FIG. 1 is a photograph of a printhead front face after a printing run showing wetting and contamination of an ink over a large area of the front face. The contaminated front face can cause or contribute to non-firing or missing drops, undersized or otherwise wrong-sized drops, satellites, or misdirected drops on the recording medium and thus result in degraded print quality.
Several material-based approaches are being explored to address this problem, such as, for example, adding hydrophobic properties to a film for use as a layer on the printhead front face. Introducing hydrophobicity usually involves integrating fluorine content into the material. However, this is generally not a straightforward procedure: blending Teflon, Viton, or custom fluorinated polymers can be challenging due to their poor solubility with the nominal components of a given film. Integrating fluorinated small molecules is generally a more facile option; however achieving a stable dispersion and the propensity for phase separation and leaching from the film are common road blocks toward implementation. Conventional approaches also include the use of low surface energy fluoropolymer-based coatings. These coatings have poor adhesion to the inkjet faceplate materials (stainless steel and polyimide) resulting in short lifetimes for the inkjet print heads. The poor adhesion of the current fluorpolymers to the stainless steel faceplate results in flaking and pealing of the coating during print head handling and cleaning. Thus, compositions, such as the SOFs of the present disclosure, where fluorine can be readily integrated (chemically bonded) and evenly dispersed within their structures offer vast improvements over conventional films, especially since the fluorine content can be logically, systematically, and easily adjusted.
Maintenance procedures have been implemented in ink jet printers for preventing and clearing ink jet blockages and for cleaning the print head front face. A maintenance procedure for ink jet printers is described in U.S. Patent Publication No. 2008/0316247, which is hereby incorporated by reference in its entirety. Examples of maintenance procedures include jetting or purging ink from the ink jet channels and nozzles and wiping the printhead front face. Jetting procedures typically involve ejecting a plurality of drops from each ink jet in order to clear contaminants from the jets. Purging procedures typically involve applying an air pressure pulse to the ink reservoir to cause ink flow from all of the jets. The jetted ink may be collected in a waste reservoir such as a spittoon. The purged ink may be collected in a waste reservoir such as a waster tray. A wetted, contaminated printhead front face interferes with the collecting of the purged ink by preventing or reducing the ability of the ink to slide over the front face into the waste reservoir. Wiping procedures are usually performed by a wiper blade that moves relative to the nozzle plate to remove ink residue, as well as any paper, dust, or other debris that has collected on the print head front face. An example of a wiper assembly is described in U.S. Pat. No. 5,432,539, which is hereby incorporated by reference herein in its entirety. Jetting/purging and wiping procedures may each be performed alone or in conjunction with one another. For example, a wiping procedure may be performed after ink is purged through the jets in order to wipe excess ink from the nozzle plate.
In view of such handling and cleaning procedures, there is a need for an inkjet faceplate material that has good adhesion to the faceplate, is thermally stable, is mechanically and chemically robust (particularly important for UV curable or other chemically reactive or agressive inks). A further need exists for an improved printhead front face coating that reduces or eliminates wetting, drooling, or flooding of ink, such as UV or solid ink, over the printhead front face. There also remains a need for an improved printhead front face coating that is robust (i.e., does not flaking and pealing of the coating during print head handling and cleaning) to withstand the various maintenance procedures applied to the printhead front face.